Particle filters for eliminating soot particles from the exhaust gas, especially of diesel combustion engines, have been used for several years. The soot particles are thereby eliminated on a filter surface, partially also in a filter structure. Particle filters provide a limited storage capacity and have to be regenerated for fixing the purification efficiency. This takes place at diesel soot particle filters (DPF) by increasing the exhaust gas temperature up to typically 600° C. to 650° C. This can happen by measures in the mixture formation of the engine, for example by postponing the main injection or by dropping an after injection that combusts in an engine or by after motor operated measures, as for example dropping an after injection that combusts at an oxidization catalyst.
An exothermic reaction is triggered off, which causes a burn-up of the soot particles and which regenerates the particle filter within several minutes. An increased oxygen content in the exhaust gas speeds up the burn-up and causes a temperature rise, which can also concern only parts of the particle filter.
A reduced exhaust gas volume also causes a temperature rise in the particle filter and speeds up the burn-up, but it can also cause local excessive temperature increases. A high material load of the particle filter can develop if the exhaust gas volume is strikingly reduced during a running regeneration process or if a high oxygen content additionally occurs in the exhaust gas like when stopping at a traffic light after a preliminary fast drive. An increased oxygen content in the exhaust gas even occurs during boost operation. The high temperatures that occur during these critical operation statuses can damage cost efficient but thermally less resilient filter materials as sinter metal or cordierite and also catalytic layers of particle filters, which are designated to reduce the temperature that is required for a regeneration.
According to the state of the art the profile of the air supply duct is reduced for reducing the oxygen content in the exhaust gas with the aid of a throttle valve in the air supply duct of the combustion engine. But the throttle valve is not completely closed at the systems that are present on the market.
EP 1 364 110 B1 describes a procedure for avoiding the overheating of a particle filter, at which a parameter is determined from control parameters of the combustion engine and/or the exhaust gas after treatment system that allows statement about the expected intensity of the reaction in the exhaust gas after treatment system. If the parameter exceeds a default threshold, measures for reducing the intensity of the reaction are undertaken. Measures are a recirculation of the air supply amount and/or an additional admeasuring of fuel and/or an increase of an exhaust gas recirculation rate. It is mentioned that the throttle valve is closed or at least partially closed for reducing the air supply amount. But an advantageous order of these measures or a simultaneous closing of the throttle valve and opening of the exhaust gas recirculation are not described.
It is known from DE 10 2004 048 135 that in order to speed up the burn-up at the regeneration of a particle filter oxygen has to be added to the exhaust gas and in order to slow down the burn-up nitrogen has to be added. The oxygen and the nitrogen are produced from the ambient air with the aid of an air decomposition device as for example a membrane that is permeable for oxygen molecules. In a compression step the supply air has thus to be brought to a gas pressure that is necessary for a sufficient passage amount. This requires an additional energy consumption, which works against an economical operation of the combustion engine.
DE 10 2006 010 095 A1 describes a procedure and a device for controlling a regeneration of a particle filter in an exhaust gas after treatment device of a combustion engine, whereby combustion supply air is added over a combustion air supply duct with a throttle valve and whereby exhaust gas is reduced over an exhaust gas recirculation and or a low pressure exhaust gas recirculation, over which exhaust gas can be added to the combustion air supply duct. It is provided according to the invention that the intervention of the throttle valve and the exhaust gas recirculation and/or the low pressure exhaust gas recirculation are undertaken in a default order. Hereby it can be achieved, that the particle filter is protected from damages by overheating and that simultaneously the driving comfort is not affected. By closing the throttle valve a low intake pressure of the combustion engine is caused, which is balanced opening the exhaust gas recirculation. It can especially be achieved by a default order of the intervention at the throttle valve and the exhaust gas recirculation that the intervention takes place torque-neutral and also acoustically imperceptible. The controlling of the regeneration process of the particle filter that is enabled by this procedure allows the use of economic materials for the particle filter such as sinter metal and cordierite.
It is especially important for thermally critical filter materials at all pre-described measures, that the temperature before the particle filter is set very accurately and that an oxygen concentration that is accommodated to the soot treatment is provided in the exhaust gas. Currently an oxygen limitation is only possible with a combination of the injection sided measures as well as interventions in the air supply system, for example by a strong throttling. If it comes to a leakage in the air supply system during this phase that has not been diagnosed so far, this can cause the destruction of the particle filter during a particle filter regeneration.
Therefore it is the task of the invention to provide a procedure for controlling the air supply system of the combustion engine, which especially has the ability to provide a diagnosis of the air supply system regarding possible defects before and after the critical particle filter regeneration. It is furthermore a task of the invention to provide a corresponding device.